How to Check if a File is Empty or Zero Bytes in Batch Script

Before processing a file in a batch script, it's often critical to verify that it actually contains data. Attempting to read from or parse an empty file can lead to unexpected errors, incorrect output, or wasted processing time. A reliable check ensures your script is robust and can handle situations where an expected data file is empty.

This guide will demonstrate the most accurate method for checking if a file is zero bytes using its size property, explain why another common method using FINDSTR is flawed and unreliable, and provide a practical example of how to use this check to control your script's logic.

The Best Method: Checking File Size with FOR

The most direct and foolproof way to determine if a file is empty is to check its size. A file with a size of exactly zero bytes is, by definition, empty. The FOR command provides a special modifier to retrieve a file's size directly.

The syntax relies on the %%~zI variable expansion, where I is the FOR loop variable.

The following script checks a file named data.txt and reports whether its size is zero.

check_file.bat

@ECHO OFF
SET "FILENAME=data.txt"

REM First, ensure the file exists to avoid a "File Not Found" error.
IF NOT EXIST "%FILENAME%" (
    ECHO File does not exist.
    GOTO :EOF
)

REM Use the FOR command to get the file's size.
FOR %%F IN ("%FILENAME%") DO (
    IF %%~zF EQU 0 (
        ECHO The file is empty (zero bytes).
    ) ELSE (
        ECHO The file has content (size is %%~zF bytes).
    )
)

Explanation:

• FOR %%F IN ("%FILENAME%") DO ...: This loop iterates once, with %%F holding the filename.
• %%~zF: This is the key. The ~z modifier expands the variable %%F to the size of the file in bytes.
• IF %%~zF EQU 0: This is a simple numerical comparison to check if the size is zero.

Examples

Scenario 1: File is Empty

REM Create an empty file for testing
TYPE NUL > data.txt

REM Run the script
check_file.bat

Output:

The file is empty (zero bytes).

Scenario 2: File has Content

REM Create a file with content
ECHO hello > data.txt

REM Run the script
check_file.bat

Output:

The file has content (size is 7 bytes).

A Common but Flawed Method to Avoid

A method you might see online involves using FINDSTR to search for any character. The logic seems sound: if no characters are found, the file must be empty. However, this approach has a critical flaw.

Let's see the Flawed FINDSTR Logic

@ECHO OFF
REM This method is UNRELIABLE.
FINDSTR . "some_file.txt" > NUL
IF %ERRORLEVEL% EQU 0 (
    ECHO "File appears to have content."
) ELSE (
    ECHO "File appears to be empty."
)

note

This uses FINDSTR . where . is a regular expression that matches any single character. If a match is found, ERRORLEVEL is 0; otherwise, it's 1.

Another Error in Action: The Flaw with Blank Lines

This method fails if a file contains content that FINDSTR . doesn't match, such as blank lines. A file with one or more newlines is not zero bytes, but this check will report it as empty.

Let's test with a file containing only a blank line.

REM Create a file that is NOT empty but has no visible characters
ECHO. > not_really_empty.txt

REM File size of not_really_empty.txt is 2 bytes (for CR/LF)

REM Run the flawed check on it
FINDSTR . "not_really_empty.txt" > NUL
IF %ERRORLEVEL% NEQ 0 ECHO Flawed check says: File is empty.

Output (This is WRONG! The file is not zero bytes.)

Flawed check says: File is empty.

Because this method produces incorrect results, it should be avoided. Always use the %%~zF file size check for accuracy.

Practical Example: Conditionally Processing a File

A primary use for this check is to prevent a script from continuing if a required input file is empty.

This script is supposed to process orders.csv. It first checks if the file exists and has content before calling the main processing logic.

@ECHO OFF
SETLOCAL
SET "ORDERS_FILE=orders.csv"

ECHO Validating input file: %ORDERS_FILE%

IF NOT EXIST "%ORDERS_FILE%" (
    ECHO [ERROR] File not found: %ORDERS_FILE%.
    GOTO :EndScript
)

REM --- The Empty File Check ---
FOR %%F IN ("%ORDERS_FILE%") DO (
    IF %%~zF EQU 0 (
        ECHO [ERROR] Input file is empty. Halting execution.
        GOTO :EndScript
    )
)

ECHO [SUCCESS] File is valid. Starting processing...
CALL :ProcessFile %ORDERS_FILE%
GOTO :EndScript

:ProcessFile
    ECHO Simulating work on file: %1
    REM (Your file processing logic would go here)
    GOTO :EOF

:EndScript
    ECHO.
    ECHO Script finished.
ENDLOCAL

Output (when orders.csv is empty)

Validating input file: orders.csv
[ERROR] Input file is empty. Halting execution.

Script finished.

Conclusion

Accurately determining if a file is empty is a simple but essential part of robust batch scripting. While several methods exist, only one is consistently reliable.

• Always use the file size property %%~zF within a FOR loop. It is the most direct, efficient, and accurate way to check if a file is exactly zero bytes.
• Avoid unreliable content-sniffing methods like FINDSTR ., which fail to correctly identify files that contain only blank lines.

By incorporating the %%~zF check into your scripts, you can prevent errors and ensure your automation handles edge cases gracefully.